Challenges in orbital current-driven domain wall motion in light metal/ferrimagnet heterostructures

Abstract: Recent advances in spintronics suggest that orbital Hall currents generated by charge injection in light metals can provide nonequilibrium angular momentum without relying on strong spin-orbit coupling (SOC). Here, we examine whether such orbital currents can drive domain wall (DW) motion in an amorphous ferrimagnetic alloy, Gd$<em>{25}$(Fe$</em>{9}$Co$<em>{1}$)$</em>{75}$ (GFC), where the rare-earth sublattice offers strong SOC for orbital-to-spin conversion. We compare three representative heterostructures: Pt/GFC as a spin Hall reference, light-metal (Mn or Ti)/GFC for direct orbital-current injection, and light-metal/Pt/GFC incorporating an ultrathin Pt layer for orbital-to-spin conversion. Whereas Pt/GFC exhibits robust and reproducible spin-orbit-torque-driven DW motion, no current-driven DW motion is detected in Mn/GFC or Ti/GFC. Second-harmonic Hall measurements nevertheless reveal finite damping-like torques in both Mn/GFC and Ti/GFC, demonstrating that angular-momentum transfer into GFC does occur but is far weaker than in Pt/GFC. Inserting a 1-nm-thick Pt conversion layer strongly enhances the damping-like torque and restores DW motion. Thickness-dependent analysis further shows that DW mobility and depinning thresholds correlate with the interfacial Dzyaloshinskii-Moriya interaction and domain-wall width, highlighting weak torque conversion and insufficient interfacial stabilization of chiral DWs as key challenges for orbital-driven DW motion in light-metal/ferrimagnet heterostructures.